Under his leadership, the theatre has become a hothouse for innovative, and sometimes controversial work work. On the eve of his departure, he looks back over his 'three acts' in the limelight Don't ask Kwame Kwei-Armah about the pressures of leadership. He'll raise his eyebrows, square his shoulders and make it clear that's never been a concern. "I'm a Black man of a certain generation," the 57-year-old artistic dir…